Improved accuracy of ultrasound-guided therapies using electromagnetic tracking: in-vivo speed of sound measurements

Vishal Samboju; Matthew Adams; Vasant Salgaonkar; Chris J. Diederich; J. Adam M. Cunha

doi:10.1117/12.2253102

22 February 2017 Improved accuracy of ultrasound-guided therapies using electromagnetic tracking: in-vivo speed of sound measurements

Vishal Samboju, Matthew Adams, Vasant Salgaonkar, Chris J. Diederich, J. Adam M. Cunha

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Proceedings Volume 10066, Energy-based Treatment of Tissue and Assessment IX; 100660P (2017) https://doi.org/10.1117/12.2253102
Event: SPIE BiOS, 2017, San Francisco, California, United States

Abstract

The speed of sound (SOS) for ultrasound devices used for imaging soft tissue is often calibrated to water, 1540 m/s¹ , despite in-vivo soft tissue SOS varying from 1450 to 1613 m/s² . Images acquired with 1540 m/s and used in conjunction with stereotactic external coordinate systems can thus result in displacement errors of several millimeters. Ultrasound imaging systems are routinely used to guide interventional thermal ablation and cryoablation devices, or radiation sources for brachytherapy³ . Brachytherapy uses small radioactive pellets, inserted interstitially with needles under ultrasound guidance, to eradicate cancerous tissue⁴ . Since the radiation dose diminishes with distance from the pellet as 1/r² , imaging uncertainty of a few millimeters can result in significant erroneous dose delivery^5,6. Likewise, modeling of power deposition and thermal dose accumulations from ablative sources are also prone to errors due to placement offsets from SOS errors⁷ . This work presents a method of mitigating needle placement error due to SOS variances without the need of ionizing radiation^2,8. We demonstrate the effects of changes in dosimetry in a prostate brachytherapy environment due to patientspecific SOS variances and the ability to mitigate dose delivery uncertainty. Electromagnetic (EM) sensors embedded in the brachytherapy ultrasound system provide information regarding 3D position and orientation of the ultrasound array. Algorithms using data from these two modalities are used to correct bmode images to account for SOS errors. While ultrasound localization resulted in >3 mm displacements, EM resolution was verified to <1 mm precision using custom-built phantoms with various SOS, showing ~1% accuracy in SOS measurement.

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Vishal Samboju, Matthew Adams, Vasant Salgaonkar, Chris J. Diederich, and J. Adam M. Cunha "Improved accuracy of ultrasound-guided therapies using electromagnetic tracking: in-vivo speed of sound measurements", Proc. SPIE 10066, Energy-based Treatment of Tissue and Assessment IX, 100660P (22 February 2017); https://doi.org/10.1117/12.2253102

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KEYWORDS

Ultrasonography

Prostate

Tissues

Sensors

Transducers

Electromagnetism

In vivo imaging

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